Swallowing is something that most of us take for granted. We drink water when we are thirsty, and swallow our morning coffee without a second thought. Yet, dysphagia (swallowing difficulty) is a serious, costly and significant health concern, particularly for the elderly and people with neurologic injuries. Dysphagia puts individuals at risk for malnutrition, dehydration and pneumonia and adversely affects quality of life. People with dysphagia have particular difficulty swallowing thin liquids safely; the fast flow of liquids makes them difficult to control. The tongue plays a critical role in containing liquids in the mouth, and in directing and controlling flow through the pharynx (throat). We are engaged in a program of research to better understand tongue function in swallowing, particularly with respect to controlling the flow of liquids. This research is guiding the development and testing of interventions with the goal of rehabilitating tongue function, so that people with dysphagia might return to swallowing thin liquids safely. To date, we have learned that modulations of the time-scale of tongue-pressure application (tongue-pressure-timing) are a critical element in liquid swallowing. Healthy young adults modulate tongue-pressure-timing across liquids of differing viscosity. We are requesting funding for the next phase in this research, to examine tongue-pressure timing in healthy adults (young and elderly) and individuals with dysphagia. The proposed research is based on the idea that the primary purpose of tongue-pressure application to a liquid stimulus is to measure and control the flow properties of that liquid. We hypothesize that, in comparison to healthy young adults, healthy seniors and people with dysphagia will demonstrate differences in tongue-pressure timing. We expect that people with abnormal tongue-pressure timing (vs. healthy young controls) will be less able to detect differences in liquid viscosity and will show reduced tongue-pressure timing modulation in swallowing across viscosity. We specifically seek to confirm that impairments in tongue- pressure-timing co-occur with impairments in the detection of viscosity differences. We also want to conduct a preliminary test of an intervention protocol that we have developed, emphasizing the modulation of tongue- pressure-timing. We hypothesize that this intervention will: a) shift tongue-pressure timing values closer to those of healthy young adults; b) facilitate improved viscosity detection; and c) improve liquid bolus control. This study will answer a critical question for the clinical management of dysphagia, namely how large must a viscosity difference be to influence swallowing function? This will inform industry standards for the formulation of thickened liquids for dysphagia. The results of this study will support the development of evidence-based clinical protocols for tongue-pressure evaluation. Finally, this study will produce preliminary evidence of the effectiveness of tongue-pressure timing training to ameliorate bolus control difficulties in dysphagia. PUBLIC HEALTH RELEVANCE: Dysphagia (swallowing difficulty) is a serious health concern for the elderly and for individuals with stroke or other neurological conditions. This study will advance our understanding of the role of tongue pressure application in swallowing, and will advise future best-practice guidelines for dysphagia assessment and intervention. The results will guide the formulation of therapeutically useful, just-thick-enough liquids and will advance our ability to address liquid bolus control difficulties, - a major component of swallowing disability.